This invention relates to fluid distribution devices.
The present invention is concerned more particularly with fluid distribution devices that are spraying apparatus, that is apparatus that breaks down liquid or a liquid/gas combination into small droplets. Spraying apparatus may also spray powders. Spraying apparatus come in a variety of forms and have been used in a variety of applications including painting, horticultural spraying and timber treatment. Spraying apparatus can however, be generally identified as falling into one of the following five classes, that is either hydraulic, pneumatic, electro-mechanical, centrifugal or thermal.
Unfortunately, there are a number of disadvantages associated with conventional spraying apparatus. It can be difficult to control the spray emerging from the spraying apparatus in terms of rate of fluid discharge, size of droplets and targeting. Although it is desirable in most situations to produce an even cloud of fine droplets, that is very difficult to achieve. Furthermore, the liquid outlets in most of the sprayers in the five classes are relatively small orifices or jets. The presence of such constrictions leads to problems with blocking unless the spray liquid is kept clear of troublesome particles. In the past on-line filtering has been used to overcome this problem but this involves extra equipment and an undesirable reduction in flow rate.
It is desirable that an electrostatic charge can be transferred to droplets emerging from a spraying apparatus as charged droplet are attracted to a spraying target which has surfaces of lower electrical potential. This attraction serves to partially overcome other forces influencing the droplet trajectories, such as frictional drag by airstream boundary effects. Therefore it can be seen that electrostatic charging adds depositional efficiency. Uniform charging of a droplet cloud has been difficult to achieve with waterbased or other conductive media, though standard in the painting industry where resistive fluids are used. With conductive fluids, either the whole apparatus, including supply tanks must be heavily insulated from earth (to withstand many kilovolts) or the high charge must in some way be earthed through the droplet cloud into the fluid column.
It is an object of the present invention to address the above problems.